1. Field of the Invention
The present invention relates to an electrical distribution track in which multiple electrically-isolated, conductive busbars are housed in an elongated enclosure for feeding higher-current electricity to take-off devices that may be inserted into the track at any point along the length of the track to make electrical contact with the busbars.
2. Background Information
It is common in factories, shops, offices and other buildings to install overhead electrical power distribution tracks for providing a convenient source of electricity for lights, machines and other electrical devices in the buildings.
Electrical power distribution tracks are typically comprised of an elongated housing containing multiple electrically-isolated, conductive busbars. Track lighting and continuous plug-in busway are typical of this type of track system. Sections of the track can be joined together to form long runs for power distribution. Take-off devices are used to tap power from the track or busway to the load apparatus. The load may be anything from a lamp to a three phase electrical machine. It is desirable to be able to insert take-off devices into, or remove them from, the track at any point along the track itself and make a secure electrical contact with the busbars.
It is also desirable that the electrical connection between take-off devices and the busbar not require bolts, crimps or other fastening hardware. A pressure connection is easily made or removed and is therefore the method of choice for most busbars to take-off device connections. However, as the ampere rating of the take-off device increases, it is necessary to increase both the contact area and pressure of the connection. Conventional systems are typically limited primarily in the contact area of the connection.
Examples of such systems may be found in U.S. Pat. No. 3,801,951, issued to Kemmerer, U.S. Pat. No. 5,619,014, issued to Seimens, or U.S. Pat. No. 6,352,450, issued to Bronk.
Commonly-assigned U.S. Pat. No. 6,039,584, issued to Ross, describes an electrical power distribution busbar, as shown in cross-section in FIGS. 1a and 1b, which employs a longitudinal, flexible, conductive member which is made of a material such as copper in order to fulfill at once the requirements of conductivity and flexibility. The flexible conductive system is captured in a busbar which carries the electrical current of the system. The current-carrying capacity is limited to the thickness of the copper which is relatively expensive compared to other conductive materials such as aluminum. Furthermore, the shape cannot be applied to larger size busbars because of cost (and reduction of flexibility) or flexible conductive systems made of aluminum because of bend radius.
For example, U.S. Pat. No. 7,374,444 issued to Bennett, teaches the use of aluminum, but the geometry is not designed to accommodate take-off devices to be installed at any point along the busway run (continuous access). Other prior art includes Multilam™, made by Multi-contact USA, as illustrated in U.S. Pat. Nos. 4,191,445 or 7,101,203 or international publication WO/2009/112762. Multilam™ bands are torsion or leaf spring contact elements. The Multilam™ design produces a large number of louvers, and therefore allows contact to be made through many defined contact points and thus is limited in its current-carrying capacity owing to fringing and other adverse effects local to the points of contact.
The prior art fails to provide a higher current-capacity busbar system which is inexpensive, robust and simple to manufacture. Thus there is still room for further improvement.